High specific energy batteries are enabled by alkali metal containing anodes. Lithium metal is particularly attractive as the anode of electrochemical cells because of its extremely high energy per unit weight, compared, for example, to anodes containing nickel or cadmium. These features are highly desirable for batteries for vehicles and portable electronic devices where a premium is paid for low weight. High specific energy batteries employ pure lithium, alloys of lithium, and intercalation compounds of lithium as anode active materials.
Both primary and secondary (non-rechargeable and rechargeable) batteries are made from lithium containing anodes. Common types of primary lithium batteries include: lithium/sulfur dioxide (Li/SO2), lithium/thionyl chloride (Li/SOCl2), lithium/manganese dioxide (LiMnO2), lithium/carbon monofluoride (Li/(CF)n), lithium/copper oxide (Li/CuO), and lithium/iodine (LiI2), and lithium anode reserve batteries (including lithium/vanadium pentoxide, lithium/thionyl chloride, and lithium/sulfur dioxide styles). Common types of secondary lithium batteries include: lithium/sulfur (Li2Sx), lithium/iron sulfide (LiFeSx), lithium/manganese titanium (LiMnTi), lithium/polymer, lithium-ion (including lithium/cobalt oxide (LiCoO2), lithium/nickel oxide LiNiO2, and lithium/manganese oxide (LiMn2O4)), lithium-vanadium pentoxide (Li/V2O5), lithium/manganese dioxide (Li/MnO2), and lithium/titanium disulfide (Li/TiS2).
Unfortunately, the reactivity of lithium also results in side reactions, resistive film formation, and dendrite formation. These destructive processes reduce performance as measured by battery charge capacity, cycle life, shelf life, specific energy, specific power, and first cycle irreversible capacity loss.
Destructive processes may be controlled by the tailored formation of a solid-electrolyte interphase (SEI) that separates the lithium anode from the electrolyte, but still conducts lithium ions. The SEI formation is the result of the chemical reaction between electrolyte components and the anode surface.
Many different solutions have been proposed for the formation of robust, yet ion conductive SEI layers. One solution is additives of agents that will oxidize lithium metal and passivate the Li surface preventing further reaction. One known solution is to saturate electrolyte with CO2. The saturation of electrolyte with CO2 gas helps to reduce voltage delay in primary cells, and also increases cycle life in secondary cells (W. B. Ebner, et al., Electrolyte For Secondary Non-Aqueous Cell, U.S. Pat. No. 4,853,304).
Similar solutions include saturation of electrolyte with SO2 gas (Y. Ein-Eli, J. Electrochem. Soc. 1996, 143, 195-197, and Nimon, et al., U.S. Pat. No. 6,632,573) and addition of ethylene sulfite (Kato, Toshimitsu, et al., U.S. Publication No. 20050181286) to improve shelf and cycle life of lithium batteries. Another example is additives of strong nitrogen containing oxidizing agents. For example, Gan, et al., describe in U.S. Pat. No. 6,060,184 and in U.S. Pat. No. 6,210,839 SEI layer enhancement for a lithium ion battery by the addition of inorganic and organic nitrates and nitrite compounds to an electrolyte comprising an alkali metal salt dissolved in a mixture of carbonate solvents. However, as will become clear to those skilled in the art, these solutions do not provide adequate redress as readily as the instant teachings.
Despite the various approaches proposed for the formation of the SEI, there remains a need for improved methods, which will allow for increased battery charge capacity, cycle life, shelf life, first cycle irreversible capacity loss, specific power, and specific energy. It is respectfully proposed that the instant disclosures address this longstanding need.